The present invention relates to the science and art of growing plants. Plant is here used in a broad sense to include trees, shrubs, bushes, flowers, crops, vegetables, herbs and the like.
The science and art of growing plants is largely empirical. Heretofore, it has been observed that the leaves of plants lacking iron will yellow. This condition is referred to as iron chlorosis or iron deficiency, and if allowed to continue in a given plant may cause its death.
It has also been observed that iron deficiency in plants is rarely due to the lack of iron in the soil. Rather, iron deficiency in plants is generally caused by some other substance in the soil making the iron unavailable to the plants. For example, iron in the form of either hematite (Fe.sub.2 O.sub.3) or magnetite (Fe.sub.3 O.sub.4) is not available to nor assimiable by plants. The presence of lime [Ca(OH).sub.2)] or other alkaline materials (pH more than 7) has been found to cause conversion of iron in the soil to one of these plant unuseable forms, i.e., either to hematite or magnetite.
Heretofore, to correct iron chlorosis in plants, the soil or the plants have been generally treated with either ferrous sulfate (FeSO.sub.4) or with a known type of iron chelate.
Ferrous sulfate itself does hold iron in a form which is available to and assimilable by plants. However, the use of ferrous sulfate to supply iron to plants and correct iron chlorosis has its drawbacks and is limited. For example, ferrous sulfate is unsuitable for use with soil containing lime [Ca(OH).sub.2 ] or another alkaline material since the alkaline material will convert the ferrous sulfate to either hematite or magnetite. Further, if a source of ammonia (NH.sub.3) is added to soil containing ferrous sulfate (as may be done to supply nitrogen to plants), the ferrous sulfate is again in this instance converted to either hematite or magnetite.
Prior art iron chelates also hold iron in a form which is available to and assimilable by plants. Such iron chelates are generally either applied to soil in which the plants are growing or to the plants as a foliar spray. Typically, these chelates are not subject to the aforementioned drawbacks associated with the use of ferrous sulfate. A significant disadvantage, however, limiting the use of most, if not all, prior art iron chelates is that they are relatively expensive to prepare and costly to buy.
It has additionally been determined that the wood of the redwood tree, i.e., sequoia sempervirens, when in a natural untreated state has an acid pH in the neighborhood of 4.5. Further, it has been found that redwood when applied to soil in a comminuted state, i.e., in the form of sawdust, chips or the like, is extremely poisonous to many plants. The exact reason for this poisonous characteristic of redwood is unknown, but it is believed that the reason is other than mere acidity. Nevertheless, it has been observed that if comminuted redwood is treated with an alkaline, such as ammonium hydroxide (NH.sub.4 OH), calcium hydroxide [Ca(OH).sub.2 ] or the like, to neutralize its inherent acidity that its poisonous characteristic disappears and the comminuted redwood then provides an excellent growing medium. Such neutralized redwood sawdust is commonly sold and used throughout California as a growing medium and soil amendment. The term soil amendment is here used to indicate a material which is added to or placed upon soil or a growing medium and as a result becomes a part thereof from which a plant feeds.
One drawback with the use of neutralized redwood as or as part of a growing medium is that it lacks plant available iron. Further, if one adds a plants source of iron, such as ferrous sulfate, to the comminuted neutralized redwood the alkaline material therein added to eliminate the poisonous characteristic of the redwood acts to convert the ferrous sulfate, as earlier mentioned, to either hematite or magnetite. Thus, heretofore, the only known way to supply plant available iron to soil containing neutralized redwood would be to use one of the relatively expensive prior art iron chelates.